Various techniques have previously been used to package integrated circuits using transfer molding equipment and procedures. Also, various lead frame designs have been used with integrated circuits, such as the flip chip design, the small outline J-lead (SOJ) packaging, and the lead-on-chip (LOC) packaging. These techniques include attaching an integrated circuit to a lead frame and wire bonds connecting the integrated circuit to conductive leads on the lead frame. The integrated circuit and lead frame are then placed into a mold and resin or thermoplastic molding compound injected into the mold cavity. Electrical components of the integrated circuit including portions of the conductive leads are encapsulated in resin or molding compound. The encapsulated package is cured, deflashed and external conductive leads prepared (trimmed, formed, coated, etc.) as required for the specific integrated circuit design. The finished product is an integrated circuit which has been encapsulated in a plastic body with electrically conductive leads extending from the plastic body. The objective of the molding process is to obtain plastic encapsulation which totally surrounds the integrated circuit and associated components with no void spaces or defects in the encapsulation.
While prior molding techniques have worked satisfactorily in packaging many integrated circuits, the advent of more complex and smaller scale integrated circuit designs has increased the importance of obtaining plastic encapsulation without any void spaces, air pockets, or other defects in the finished integrated circuit package. Incomplete filling of the mold cavity with resin or void spaces within the encapsulation will result in a defective product.
Conventional transfer molding techniques use a mold with two sections or halves that are secured to opposite sides of the integrated circuit and its associated lead frame. The mold halves are securely clamped together (sandwiched) about the integrated circuit and lead frame. Conventional molds have an opening (mold flow gate) in either the top half of the mold or the bottom half of the mold for injection of the molding compound. A portion of the mold opposite the injection point (flow gate) usually has one or more small air vents to allow air and other gases to escape from the mold cavity as the resin is injected. The pressure drop which occurs at the mold flow gate and resin flow therethrough frequently cause erosion and wear at the injection opening in the mold. Erosion of the injection opening (bottom gate or top gate) limits the useful life of the mold.
The small openings used for air vents in conventional molds frequently become plugged. Plugging of the air vents will either reduce the life of the mold or require increased maintenance to open any plugged air vents. As integrated circuits are reduced in size (become thinner), more air or other gases must be displaced from the cavity of existing molds which increases the opportunity for plugging. Designing new molds for each new change in dimensions of an integrated circuit is very expensive and time consuming.
A need has arisen for a lead frame with slots to improve resin fluid flow during the molding process, to provide uniform encapsulation of an integrated circuit package and to improve the useful life of the mold.